This invention relates generally to thin-walled metal tubes and methods and apparatus for manufacturing the same by a single impact extrusion operation.
More particularly, the invention relates to a punch and die apparatus which permits a stable mass production of thin-walled metal tubes, each tube having a barrel wall thickness in the range of about 20 to 70 microns by a single extrusion operation, a method of producing such thin-walled metal tubes having a barrel wall thickness of 20 to 70 microns by a single extrusion operation with the punch and die apparatus, and to a thin-walled metal tube having a barrel wall thickness ranging between about 20 and about 70 microns having a particular physical characteristic in the border section between the barrel section and the shoulder section thereof.
Collapsible tubes having diameters on the order of about 35 millimeters are well known and are in general use as containers for liquors or pastes. Such conventional collapsible tubes generally comprise a thin-walled metal tube having a wall thickness ranging between about 20 and about 70 microns, the metal tube being coated at its inner and/or outer surface with a layer of plastic having a thickness ranging between about 50 and about 500 microns.
Such conventional composite collapsible structures have moderate pressing characteristics, as well as restoration characteristics, and also have good air and vapor-barrier properties thereby avoiding excessive air-back phenomena. Additionally, such conventional composite collapsible tubes are simple to handle during manufacture and transport and have an atractive appearance. All of these features combine to enhance the commercial value of such composite collapsible tubes.
Laminated tubes including metal foil layers are utilized as collapsible tubes and also have the features discussed above at least to some extent.
However, in such laminated tubes, a longitudinally extending side seam is inevitably formed in the tube body during manufacture. Additionally, the shoulder and barrel sections of the laminated tube are usually separately fabricated and then subsequently joined together. Accordingly, it is not uncommon for such tubes to break or tear along the side seam or joint line between the shoulder and barrel sections.
Since the side seam is typically effected by means of a heat seal, only a thermoplastic resin can be utilized as the coating plastic. Further, such laminated tubes cannot be used as containers for material which requires heat sterilization. A further disadvantage is that such laminated tubes usually exhibit an inferior gas-barrier characteristic at its shoulder section.
In order to overcome these disadvantages of laminated tubes, there is a need for a seamless unitary metal tube which has a barrel wall thickness in the range of about 20 to about 70 microns.
A method for manufacturing a unitary metal tube by a single extrusion operation utilizing punch and die apparatus is disclosed in U.S. Pat. No. 2,112,085.
However, in such conventional method of producing metal tubes by single impact extrusion methods, such for example as in the method disclosed in the above-mentioned patent, it is not possible to reduce the thickness of the barrel wall to less than about 75 microns even in the case of tubes having relatively small diameters for various reasons such, for example, as breakage or tearing of the tube, wrinkles being formed therein due to elongation of the metallic material or breakdown of the punch and die apparatus.
Thus, it has heretofore not been possible to produce in a stable fashion on an industrial production scale a unitary metal tube having a barrel wall thickness in the range of between about 20 and 70 microns and which is suitable for all materials.
Various attempts have been made to satisfy the above requirements. One such attempt is disclosed in U.S. patent application Ser. No. 900,969, now U.S. Pat. No. 4,200,051, wherein a method is disclosed including a first step of manufacturing a primary product by an impact extrusion process or, alternatively, by at least one of a deep drawing, necking, burring and junctioning, and a second step of effecting a secondary product by ironing which employs the use of a specific die ring. According to this method, it is possible to produce a thin-walled metal tube having a barrel wall thickness ranging between about 20 and about 70 microns and which has favorable properties and which is manufacturable in a stable fashion in industrial quantities.
However, this method requires more then two separate steps of plastic working and, therefore, is relatively complicated and expensive thereby giving rise to a necessity for a simpler production method.
Additionally, in the manufacture of a composite tube by coating the metal tube with a plastic layer, the plastic layer is undesirably thinned at the border section between the barrel section and the shoulder section due to the flow of the molten plastic thereby resulting in a deterioration of the mechanical strength at the border section. This deterioration in turn results in problems such as exposure of the metal tube due to wear or bending resulting from contact with a hard member, generation of pin holes or breakage in the vicinity of the border section, and/or collapse or deformation of the tube during transportation particularly when the tubes are transported in a vertical posture.
In view of the foregoing, there is an increased demand for a method providing the capability of manufacturing a thin-walled metal tube in an uncomplicated manner while eliminating the above-mentioned problems inherent in prior art manufacturing techniques.
In order to meet this demand, the present invention comprises a device having the capability of producing thin-walled metal tubes having a barrel wall thickness of about 20 to about 70 microns by a single impact extrusion operation. Further, a method of producing such tubes utilizing the apparatus is also disclosed.